Bistable multivibrator means



June 28, 1966 M DONNER 3,258,762

CONTROL AND ALARM SYSTEMS Filed Feb. 5, 1965 (/0 (l f2 y I mi o1 GEoPHoNE AMF! FILTER I I T1 l f D2 y '7v--I- ALARM SYSTEM l F iEJb VOLTAGE Q TIME United States Patent O 3,258,762 CONTROL AND ALARM SYSTEMS Meier Donner, Paris, France, assigner to Compagnie Generale de Geophysique, Paris, France Filed Feb. 5, 1965, Ser. No. 430,674 4 Claims. (Cl. 340-261) This invention relates to control and alarm systems and is more particularly `a continuation-in-part of my application for Electric Allarm System, Serial No. 117,- 002, filed June 14, 1961 and now abandoned.

An object of the invention is to provide improved control and alarm systems. It is -another object of the invention to provide an improved alarm system adapted to detect the passage or tentative passage of any unauthorized person entering a predetermined area, whether enclosed or not enclosed, -or else, to signal any attempt of breaking through doors, closures and the like, or any tentative damage to any plant, apparatus, public works, machines, etc.

It has already been proposed to provide alarm systems for signalling any attempted passage through enclosures by fitting on such enclosures microphones connected with a control station provided with alarm means. Such microphones carried by the enclosures above ground are actuated yby the acoustic vibrations produced by the attempted passage through the enclosure and they transmit the information to the central station.

Such arrangements require the presence of an enclosure, the cost price of which may be comparatively high, chiefly if the periphery of the area to be protected is large. Furthermore, such a system has the drawback that, by reason of the microphones being secured to the enclosure, they are generally apparent to view or, at least, their presence may be suspected so that any person who attempts breaking through the enclosure may rst seek to neutralize their action.

According to the invention, these drawbacks are removed by replacing microphone-s arranged above ground by geophones buried under ground.

It is a well known fact that when Kgeophysically prospecting, it is now possible Ito use highly sensitive geophones which are furthermore watertight, of a very reduced weigh-t and of a comparatively low cost price.

The invention contemplates employing such under ground geophones which are consequently perfectly visible, as detectors of vibrations of any desired range of frequencies.

Experience shows that the geophones used at the present Itime are sufficiently sensitive and can signal the passage of a person moving in proximity to the location of such geophones.

It is therefore sullicient to arrange geophones along each passageway, each of the geophones being spaced from the adjacent geophones by a distance which is less than twice its operative radius, so lthat the geophones may form a line which it is impossible to pass without actuating at -least one geophone.

Furthermore, lthe geophones are in practice sensitive to frequencies which are as well infra acoustic and acoustic, whereby a further advantage is obtained over microphones.

Experience has shown Ithat the vibrations produced by the passage of a person or -of an animal, are transmitted with a better effect through loose ground, such as gravel or broken stones, than through a compact ground.

Consequently, the invention provides the positioning of the geophones, by way of preference, inside a layer of gravel or broken stones of a thickness of say 10 to 20 centimeters and of a breadth of l to 2 meters. The layer of broken stones or gravel may be covered by a layer of earthcarrying grass or otherwise, so as to completely conceal the layer.

A-s a modication, the geophones may be associated with an enclosure. in such a case, they are preferably secured to a buried section of the supports of the enclosure, whereby they may be subjected directly to the vibrations transmitted by such supports together with the vibrations transmitted by the ground.

According to a f-urther modification, the geophones are positioned inside a trough covered by a rigid metal plate, which plate may itself lbe covered by a thin layer of earth, so that Vit may conceal the existence of said plate.

Experience has also shown that the useful vibrations are properly transmitted through such a trough and are received by the rigid metal plate which forms a sort of vibration ampliiier.

The trough considered may be given any desired shape and it may even be constituted by a series of hollow tubes -arranged endwise, the geophones being housed'inside the tubular system and secured to the inner wall of the la-tter.

Other modifications in the positioning of the geophones are described hereinafter.

The invention further contemplates that the vibrations collected by the geophones be amplified and suitably iiltered in a manner such as to transmit only the useful signals while removing the parasitic signals; the signals thus filtered act on an electron-ic bistable multivibrator or iiip op, of which one stable condition forms the normal condition, while the second condition forms the relaxed condition, the multivibrator in this second condition controlling the actual alarm system such as a luminous signal, an acoustic signal or the like.

Consequently, the multivibrator changes from the rst condition to the second condition whenever the voltage applied across its input rises, even transiently, above a predetermined value considered as its operative threshold.

According to a feature of the invention and with a view to removing as `far as possible the possibility of an untimely release or Itriggering of the multivibrator, while retaining an alarm system having the desired sensitivity, the threshold of the multivibrator is adjustable and there are provided means for the automatic control thereof with a view to modifying thevalue of 'the threshold, depending on the parasitic noises which distinguish from the signals produced by an attempted passage or breaking through the enclosure by a slower progression of their amplitudes.

Experience has, in fact, shown 'that the usef-ul signals collected by the geophones and produced by an attempted breaking through or passage are characterized by a very fast rise, whereas parasitic signals do not show such a sudden rise.

Consequently the invention resorts to this difference in waveform, 'by modifying automatically the value of the threshold on the one hand, as a function of the average intensity of the incoming parasitic noises and, on the other hand, as a function of the gradient of the collected signals.

The auto-matic adjustment of the threshold reduces the sensitivity of the multivibrator for parasitic noi-ses, that is, for the oscillations of which the amplitude changes only slowly. tln contradistinction, the automatic adjustment of the threshold is such that the arrangement retains its full sensitivity for the signals having a steep wave front such as those produced by an attempted passage or breaking through an enclosure.

The invention will now be disclosed with further detail,

reference being had to the accompanying drawings illustrating, by way of example and by no means in a limiting sense, Various embodiments of said invention. In said drawings:

FIGURE 1 shows a geophone fitted inside a trough;

FIGURE 2 illustrates a geophone secured to an iron rod;

FIGURE 3 illustrates an alarm system established in conformity with the invention; and

FIGURE 4 shows voltage waveforms as a function of time to explain signal discrimination provided by the system.

A trough 1 is buried in the ground and is bounded by walls which may be consitituted by masonary 2, for instance. Trough 1 is covered by a metal sheet 3 which is covered preferably by a layer of earth 6. To the lower surface of the metal sheet 3 is secured a member 4 carrying the actual geophone 5. Thus the geophone collects the vibrations transmitted by the metal sheet 4 and also by the air passing through the trough. Experience shows that the metal sheet forms with the masonry wall a medium for producing a dampening, and for consequently transmitting the vibrations substantial distances. Furthermore, the metal sheet forms, to a certain extent, an amplifier for the vibrations.

As a modification, the buried geophones are rigidly carried by iron rods of the type serving for the reinforcement of concrete. The rods are buried horizontally and their role consists in transmitting to the geophones the vibrations of the ground.

FIG. 2 shows diagrammatically an embodiment of such a type, including a buried rod 7 having a geophone attached to its central portion.

According to a further modification, the geophone is secured to a slightly buried wire which is stretched by any suitable means.

The wire may be, for instance, of steel and its energization is produced by the steps of a person walking in proximity therewith. As a matter of fact, such walking produces vibrations of the ground, which are communicated to the stretched wire and are propagated through it until they reach the geophone which is thus acuated.

FIG. 3 shows the now preferred embodiment of an alarm system according to the invention. The alarm system includes a geophone 10 acting on an amplifier 11. Only one geophone has been illustrated, but in practice the same amplifier may be actuated by a plurality of geophones arranged either in series or in parallel, or again, as a series-parallel arrangement. The signals amplified by amplifier 11 pass through a filter 12 which allows only the useful frequencies to pass. In practice, the elements 11 and 12 may be combined to form a frequency-selecting amplifier.

The output of the filter 12 feeds the input of an electronic bistable multivibrator means 14 through a rectifier 13, so that the voltages applied to multivibrator means 14 remain always of the same polarity, the one for which multivibrator means 14 is sensitive.

Furthermore, the output of the filter 12 is connected with the input of an amplifier 16 feeding a rectifier 17, followed by an integrator 18, which latter is constituted chiefiy by a capacitor which is thus charged in accordance with the rectifier voltage through a resistance.

The output Voltage of the integrator 1S acts on the multivibrator means 14, so as to modify the value of its operative threshold.

The output of the multivibrator means 14 acts on an alarm system of any suitable type; once the multivibrator means 14 is triggered, the alarm system 15 operates permanently until an operator returns the multivibrator means 14 into its normal original condition by control means.

The threshold value for operation of the multivibrator means 14 is an increasing function of the voltage proi vided by the integrator 18, the insertion of the elements 16, 17, 18 being such that the threshold is an increasing function of the average level of the parasitic noises at the output of the filter 12, appearing at the moment of the incoming of the useful signals.

In contradistinction, in the case of a rapid rise of the signal at the output of filter 12, and as a consequence of the waveform modification provided by the presence of the integrator 18, the voltage applied by integrator 18 does not then practically vary so that the threshold remains constant, whereby the system as disclosed hereinabove is particularly sensitive to the signals having a comparatively steep wave front.

More particularly, the integrator transforms a signal with a steep front, i.e., a signal whose amplitude varies as a function of time according to the curve 18 shown in FIG. 4, into a signal whose variation is much slower, i.e., whose amplitude varies as a function of time according to the broken line curve 2i) of FIG. 4.

It follows therefrom that the voltage difference between the signals fed to multivibrator means 14 from rectifier 13 and integrator 18, which is equal, with the exception of one non-essential factor, to the difference of the ordinates of the curves indicated by the solid line 19 and by the broken line 20, increases rapidly and then decreases. In particular, it passes through a maximum at point 21, and when said maximum reaches a predetermined value, the bistable multivibrator means 14 is triggered and actuates the alarm system 15.

In contrast thereto, in the case of signals which vary slowly, the integrator 18 exerts practically no action, and the difference of the ordinates of the curves indicated by the solid line 19 and by the broken line 20 is very small and does not reach the threshold value at which the bistable multivibrator means 14 is triggered.

The details of the blocks of FIG. 3 will now be described in detail.

Geophone 1f) may be one of many available geophones such as used in oil prospecting. Amplifier 11 is a con- Ventional voltage amplifier. Filter 12 can be any appropriate active or passive filter network.

Rectifier 13 comprises a full-wave rectifier with two diodes D1 and D2 supplied from the secondary of a transformer TR1, whose primary is connected to the output of filter 12. The output of the full-wave rectifier feeds the base of PNP transistor T 1 operating as an emitter follower impedance transformer.

Amplifier 16 is a common emitter amplifier employing PNP transistor T2. Rectifier 17 is a full-wave rectifier including diodes D3 and D4, whose cathodes are connected to the centertapped secondary of transformer TR2. The primary of transformer TR2 is connected to the collector of transistor T2.

Integrator 1S includes the capacitor C1 connected between the junction of the anodes of diodes D3 and D4 and ground; and the emitter follower amplifier, comprising transistor T3, whose base is connected to the ungrounded end of capacitor C1. The capacitance of capacitor C1 is chosen so that it integrates the signals from rectifier 17.

The multivibrator means 14 comprises a bistable multivibrator including NPN transistor T6 and PNP transistor T7. The bistable multivibrator is a conventional flip fiop which is set by a signal received at the base of transistor T6 and reset by the opening of switch SR in the emitter circuit of transistor T7. The collector circuit of transistor T7 includes the coil of relay RA which controls the alarm system 15. The remainder of means 14 is a differential amplifier comprising two transistors T4 and T5, the emitters of which are connected to a source of positive potential through a resistor R16. As shown in the drawing, the base of transistor T4 is connected to the output of integrator 18 (emitter of transistor T 3) through a resistor R15; and the output of rectifier 13 (the emitter of transistor T1) is connected to the base of transistor T5. The collector of transistor T4 is grounded and the collector of transistor T5 is grounded through a resistance R17. Moreover, a capacitor C2 connects the collector of transistor T5 to the base of transistor T4.

This differential amplifier operates somewhat in the manner of a monostable multivibrator and these two transistors constitute what is referred to in the literature as a long-tailed pair. It is known that in such a circuit the conductivity of the trans-istors T4 and T5 depends above all on the difference of potential between the bases of the two transistors T4 and T5.

When the geophone supplies no signal, transistor T4 is conductive, transistor T5 is blocked and the potential of the base of transistor T4 is negative relatively to the base of transistor T5. Consequently, the collector of transistor T5 is at ground potential. When a steep wave front signal appears at the terminals of filter 12 there is immediately a negative impulse at the output of rectilier 13, because the response of the latter is instantaneous. In contrast, the output voltage of integrator 18 is not modified because condenser C1 takes time to acquire a charge, so that the potential of the base of transistor T4 remains unchanged.

If the negative impulse supplied by the rectifier 13 is of suflicient amplitude, transistor T5 becomes conductive and a voltage appears across the terminals of resistor R17 and is returned to the base of transistor T4 by the condenser C2, thereby further blocking transistor T4.

The voltage across resistor R17 controls the bistable multivibrator consisting of transistors T6 and T7, causing a current to flow in the winding RA of the relay operating to actuate the alarm system 15.

If the geophone 10 supplies voltages which increase only slowly, as a function of time, the voltages in the terminals of rectifier 13 and integrator 18 vary similarly, and the differential amplifier, including transistors T4 and T5, remains in the same state; the voltage across resistor R17 is zero and the bistable multivibrator comprising transistors T6 and T7 remains unchanged. Consequently the alarm system is not actuated.

Of course, the alarm system 15 may be associated with auxiliary means controlled by the operator, so as to be connected as desired with the alarm system 15, which allows an analysis of the signals collected by the geophone .and which have produced at the start the change of state of the multivibrator. For instance, the auxiliary means may be constituted by a continuously operating indicator, listening means, a loudspeaker, an oscillograph of -the cathode ray type, for instance, a photographic recorder, or the like.

What is claimed is:

1. An alarm system comprising detection means sensitive to vibration, a bistable multivibrator including difference amplifier means, amplifying and filtering means connected between said detection means and said difference amplifier means for feeding to the latter signals from said detection means, rectifying means for receiving an output from said ltering means, an integrator connected to said rectifying means and in turn connected to said difference amplifier means to control actuation of the bistable multivibrator by controlling the amplitude of the signal necessary to actua-te the multivibrator, said integrator being effective to integrate the signal transmitted from said detection means lto said bistable multivibrator whereby Vibration having a steep waveform will actuate said multivibrator, an-d alarm means connected to said multivibrator for being energized when said multivibrator is actuated.

2. In combination, first means for receiving an amplitude varying signal, second means connected to said first means for filtering said amplitude varying signal to transmit only signals having a given range of frequencies, first rectifier means connected to said second means for rectifying the signal transmitted by said second means, second sectifier means connected to said second means for rectifying the signal transmitted by said second means, integrating means connected to said second rectifying means for integrating the rectified signal, difference amplifier means including a first input connected to said first rectifying means, a second input connected to said integrator means and an output for transmitting a signal when the difference between the Iamplitude of the signal received from said first rectifyng means exceeds the amplitude of the signal received from said integrating means by a given amount, and bistable means connected to the output of said difference amplifier means, said bistable means changing stable states when said difference amplifier means transmits a signal.

3. The apparatus of claim 2, wherein said bistable means has first and second stable states and wherein said bistable means is triggered to said second stable state upon receipt of a signal from said difference amplifying means, and further comprising alarm means connected to said bistable means and operative when the latter is in said second stable state.

4. The apparatus of claim 3 further comprising means connected to said bistable means for forcing the latter to said iirst stable state.

References Cited by the Examiner UNITED STATES PATENTS 2,329,570 9/ 1943 Wellenstein. 2,435,996 2/1948 Baird. 2,730,896 1/ 1956 De Boisblanc. 2,731,520 1/ 1956 Richardson. 2,832,915 4/1958 McCoy 340-261 X 2,907,012 9/ 1959 Pitman 340-213 2,942,247 6/ 1960 Lineau 340-261 X 2,991,458 7/1961 Cooke 340-258 X 3,027,467 3/ 1962 Lipman 340-258 X 3,095,730 7/1963 Matheson.

FOREIGN PATENTS 942,848 11/ 1963 England.

NEIL C. READ, Primary' Examiner.

R. M. GOLDMAN, Assistant Examiner. 

1. AN ALARM SYSTEM COMPRISING DETECTION MEANS SENSITIVE TO VIBRATION, A BISTABLE MULTIVIBRATOR INCLUDINGA DIFFERENCE AMPLIFIER MEANS, AMPLIFYING AND FILTERING MEANS CONNECTED BETWEEN SAID DETECTION MEANS AND SAID DIFFERENCE AMPLIFIER MEANS FOR FEEDING TO THE LATTER SIGNALS FROM SAID DETECTION MEANS, RECTIFYING MEANS FOR RECEIVING AN OUTPUT FROM SAID FILTERING MEANS, AN INTEGRATOR CONNECTED TO SAID RECTIFYING MEANS AND IN TURN CONNECTED TO SAID DIFFERENCE AMPLIFIER MEANS TO CONTROL ACTUATION OF THE BISTABLE MULTIVIBRATOR BY CONTROLLING THE AMPLITUDE OF THE SIGNAL NECESSARY TO ACTUATE THE MULTIVIBRATOR, SAID INTEGRATOR BEING EFFECTIVE TO INTEGRATE THE SIGNAL TRANSMITTED FROM SAID DETECTION MEANS TO SAID BISTABLE MULTIVIBRATOR WHEREBY VIBRATION HAVING A STEEP WAVEFORM WILL ACTUATE SAID MULTIVIBRATOR, AND ALARM MEANS CONNECTED TO SAID MULTIVIBRATOR FOR BEING ENERGIZED WHEN SAID MULTIVIBRATOR IS ACTUATED. 